It is recalled in particular that in liquids, turbidity is the result of non-dissolved matter that is finely dispersed: it can be determined by measuring the decrease in the intensity of light flux as it passes through the liquid in which part of the light is absorbed, or by measuring the intensity of the light that is diffused, and in particular at 90.degree.; light diffusion is a property of liquids which can be used for measuring such turbidity; the above-referenced European standard describes four optical methods for determining water turbidity to obtain information on site about surface water, potable water, and residual water. Since turbidity is an overall parameter for determining the level of pollution or the effectiveness of an industrial method, the present invention can have numerous applications, such as:
monitoring waste at the outlet from sewage stations, in terms of cloudy residual water; PA1 monitoring sewage methods or industrial methods; PA1 determining the quality of water in settling tanks, in river water, and in lake water; PA1 detecting operating anomalies with filters, industrial separators; PA1 monitoring industrial effluents, and in particular oil effluents; PA1 monitoring deballasting by oil tankers; and PA1 monitoring discharges of bilge water into the sea by ships. PA1 ultrasound waves are generated in all directions around the emitting and receiving optical/liquid interfaces of said optical pieces in contact with said liquid, thereby cleaning said interface surfaces or preventing them from becoming dirtied, in particular when gaseous microcavities created in this way in the liquid implode; and PA1 the emission of said ultrasound waves is stopped and a measurement is taken of the light received by the cell.
Numerous equipments have thus been developed to enable the turbidity in an aqueous medium to be measured, and more recently to comply with the above standard; some such apparatuses have constituted the subject matter of patent applications, such as application EP 596231 published on May 11, 1994 and international application WO 9800701 published on Jan. 8, 1998, which describe the combination of a nephelometer and a turbidimeter; it is recalled that nephelometry relates to measuring the concentration of an emulsion on the basis of its transparency.
Although those optical measurement apparatuses give full satisfaction concerning optically measuring the intensity of a given light after it has traveled a determined distance through the liquid under inspection, measurement proper is often spoilt by the fact that dirt such as oil can become deposited on the surfaces of the optical interfaces immersed in the liquid; the interfaces serve firstly to emit light into the liquid and secondly to receive light therefrom for measurement purposes: at present, methods and devices based on windshield-wiper principles are unsatisfactory and require assiduous maintenance.